It is impossible to retrieve the Bitcoins if you have lost the Private key.

The lost Bitcoins won’t disappear or go away from the address, but will stay there forever.

So what happens to the lost Bitcoin?

Literally nothing. The fund will be dormant.

As it is impossible for anyone to find a Private Key, the fund will be untouched and removed from the market, as in out of circulation.

Theoretically, this will eventually lead to the higher price Bitcoin as the “demand” will get higher than “supply”.